Metpetruby
Corundum-forming reaction in the Fiskenæsset complex: forsterite/serpentinite from ultramafic rocks in contact with anorthositic rocks react with cross-cutting pegmatites to form a range of new minerals, including pargasite (green) or anthophyllite (silver-brownish), spinel (red) or ruby/sapphire or sapphirine (greyish-blue), biotite and/or black amphiboles.

Ruby formation and fingerprinting

Pink sapphire and ruby (corundum) have been discovered in more than 40 localities in the area near Fiskenæsset (Qeqertarsuatsiaat), southern West-Greenland. A few localities yield stones of gem quality, especially in the area near Aappaluttoq. GEUS has investigated the pink sapphire and ruby from these localities together with MMR, Nuuk, Greenland. Furthermore, we are investigating the red corundum in the Nattivit area, East Greenland, as part of an ongoing PhD-project.

GEUS also investigated ruby and pink-sapphire occurrences in Tanzania in a project focused on sustainable and artisanal small-scale mining. Smaller investigations in a range of other localities on Greenland's west coast have been carried out.

Geochemical and optical fingerprinting of ruby and sapphire is done to establish the stones' country of origin. Fingerprinting of gemstones, for example, rubies, has been performed for economic, political, and scientific reasons. The country of origin of a gemstone is a factor determining its market value, irrespective of quality aspects like colour, cut or clarity. Governments have an interest in fingerprinting for taxation reasons. Some customers actively seek conflict-free (no war, no child-labour, environmentally safe) gemstones.

From a scientific point of view, fingerprinting reveals important information on the geological history of these gemstones. To fingerprint the characteristics of these minerals, GEUS applied trace-element geochemistry with LA-ICP-MS, oxygen isotope investigations and an analysis of optical features and uncommon inclusions with optical microscopy.

Corundum from the Fiskenæsset complex formed in an ultramafic rock-anothosite-pegmatite setting, which is uncommon worldwide (above). Therefore, the rocks have a special trace-element pattern, isotope geochemistry and uncommon mineral inclusions and growth features, which give the ruby and sapphire from the Fiskenæsset complex some unique fingerprinting characteristics.

Nynke Keulen

Senior Researcher
Petrology and Economic Geology
Phone: +45 91333873